P0240

What it means

P0240 is the generic SAE J2012 code for a range or performance problem in the boost pressure sensor B circuit on a turbocharged or supercharged engine. The control unit has compared the signal from sensor B with another source, such as the primary boost sensor, the barometric or manifold pressure reading, or the expected value for the engine's operating condition, and found it implausible. The signal is still within electrical limits, so this is a plausibility fault rather than a simple open or short circuit.

Symptoms

• Engine warning light on
• Reduced power or limp mode
• Poor or uneven acceleration
• Turbo boost feels lacking or surges
• Black smoke or rough running under load
• Possible turbo-related fault codes stored alongside

Possible causes

• Blocked, split, loose or disconnected boost sensor hose or charge air pipework leak near the sensorlikely
• Faulty or contaminated boost pressure sensor B (drifting or sluggish signal)likely
• Wiring or connector fault at the sensor, such as corrosion, high resistance, chafing or a poor terminal fitpossible
• Boost control fault, such as a sticking wastegate or variable geometry mechanism, or a faulty actuator or control valve causing real over- or under-boostpossible
• Charge air leak or restriction (intercooler, hoses, clamps, blocked air filter or intake) causing a genuine mismatch between sensorspossible
• Fault in the reference sensor used for comparison, for example the primary boost, manifold pressure or barometric sensorpossible
• Control unit fault or outdated calibration, where a known software issue is documented for the specific modelrare

How to diagnose

1. Read all stored and pending codes and the freeze frame data, noting load, engine speed and boost values when the fault set, and check for other boost, MAF or turbo codes.
2. Visually inspect the sensor, its vacuum or pressure hose, the connector and wiring for damage, oil contamination, loose fittings and chafing.
3. Inspect the air filter, intake ducting, intercooler and all charge air hoses and clamps for splits, oil leaks or looseness.
4. With the ignition on and engine off, compare sensor B's reading with the other pressure sensors and barometric pressure; they should closely agree.
5. Check the sensor's supply voltage, ground and signal wiring for continuity, resistance and shorts, following the manufacturer's wiring data.
6. Monitor live boost data on a road test or under load and compare actual with requested boost to find real over- or under-boost.
7. Smoke or pressure test the charge air system, and check the wastegate or variable geometry actuator movement and control, as the procedure depends on the engine.
8. Check for applicable service bulletins or software updates for the model if no hardware fault is found.

How to fix

• Repair or replace split, loose, blocked or disconnected hoses, pipes and clamps on the sensor and charge air system.
• Replace the boost pressure sensor B if its readings are out of range or it is contaminated.
• Repair damaged wiring, terminals or connectors, and clear the fault only after the repair.
• Repair or replace the faulty wastegate, variable geometry mechanism, actuator or control valve causing incorrect boost.
• Replace a faulty reference pressure sensor if it is the one reading incorrectly.
• Apply a manufacturer calibration update only where an outdated or faulty calibration is a documented cause for that model.

Can I keep driving?

Nearby codes

• P023FGenericFuel Pump Secondary Circuit/Open
• P0241GenericTurbocharger/Supercharger Boost Sensor B Circuit Low